Two thirds of Northern Ireland's forests are under threat from a killer tree disease.

The fungal disease P. ramorum (often called Sudden Oak Death) has already infected tens of thousands of Japanese larch trees.

This has led to the felling of over 200 hectares across nine woodlands.

The disease may have jumped species and has infected a Sitka spruce in the Republic of Ireland and several beech trees in County Down, in the north.

If the disease spreads to other Sitka trees it could be a disaster for the Northern Ireland Forestry Service. The species makes up two thirds of all government-owned forests in Northern Ireland.

The disease was already known to be able to infect beech trees. It has also been confirmed that the infection has been found in European larch in England.

There is little the Forestry Service can do but sit and wait and watch.

When I walked some of the infected woodlands in Northern Ireland it was clear that some species near heavily diseased larch were showing signs of distress. But this was more than likely caused by their foliage being overwhelmed by the fungal spores rather then being infected.

Ultimately the disease can only be confirmed by laboratory tests. But it leaves the service with a lot more trees to monitor.

A spokesperson for the Northern Ireland Department of Agriculture said there is cause for concern and that they would be increasing their inspections: "We are responding to these developments by adapting our planned surveillance to take in Sitka spruce in areas where Japanese larch and Rhododendron have been infected and to widen our surveys of Japanese larch to include all larch species."

The disease is thought to have been imported into the UK and Ireland by infected rhododendron plants.

The diseased Sitka spruce in the Republic of Ireland was found under the canopy of a diseased rhododendron bush.

Scientists are being guarded in their hope that it could just be a freak infection, although tests in international trials showed that Sitka spruce were susceptible to the disease.